BLASTING DEVICE WITH ADJUSTABLE BLAST STRENGTH

Abstract: The invention relates to a method for blasting with sand or a like blasting medium, wherein the blasting medium is conducted from a storage vessel (1) to a spray nozzle (6) and distributed by means of a pressure medium such as compressed air or water, and wherein according to the invention the blasting medium is conducted from the storage vessel (1) by means of pump means (2) and the blasting medium is preferably mixed with water (13, 14, 15... 22<1>, 23<1>, 20) in the vessel (1) and kept in saturated solution in the storage vessel by means of agitating or mixing means (4, 26, 27, 28... 31, 32).

Description: Title: Blasting device with adjustable blast strength The invention relates to a method for blasting with sand or a like blasting medium, wherein the blasting medium is conducted from a storage vessel to a spray nozzle and distributed by means of a pressure medium such as compressed air.or water. For cleaning surfaces of for instance stone or metal, sand or a like blasting medium is typically used which, by means of a blasting device, is sprayed under pressure against the surface to be cleaned. For this, at least the pressure to be used and the nature of the blasting medium should at any rate be adapted to the surface to be cleaned, because damage to the surface has to be prevented. For blasting surfaces, methods are used that are based on different principles. In a known method, dry blasting medium is supplied near a spray nozzle, which blasting medium is drawn from a storage vessel by passing a pressure medium such as air or water through the nozzle at high velocity, thus creating a partial vacuum in a feed line for the blasting medium. This method has the advantage that a great capacity can be achieved, but it can only be utilized for relatively hard blasting, with the use of much pressure medium and little blasting medium. In this connection, hard is to be understood to mean (highly) corrosive. This method has as a further drawback that dry blasting medium should always be fed and that an excess pressure medium should be supplied for generating the desired partial vacuum. Moreover, if water is used as pressure medium, such a method produces much contaminated water that should generally be discharged as chemical waste, which is costly and involves a substantial environmental burden. An additional drawback of this method is that at least two hoses should be connected near the spray nozzle, which complicates the use of the spray nozzle at a distance from the further blasting device. In a further known method, blasting medium in a storage vessel is put under high pressure by means of a pressure medium such as air or water and fed from there to the spray nozzle, also under pressure. Typically, in the spray nozzle an additional pressure medium in the form of compressed air is fed, enabling operating with relatively much blasting medium and much or little pressure medium. Depending on the choice of the pressure medium, this known method permits either hard or soft blasting; when (much) water is used, soft blasting takes place and when air and dry blasting medium are used, hard blasting takes place. In this connection, 'soft' should be understood to mean relatively little corrosive. The use of a storage vessel to be pressurized has a number of significant drawbacks. For instance, the storage vessel should always be completely filled, as a consequence of which, after the use has ended, the storage vessel is completely filled with pressure medium that cannot be reused due to contamination, which involves a significant environmental burden. Moreover, the extent of filling cannot be adapted to, for instance, the size and extent of contamination of the surface to be blasted, a fixed proportion between the blasting medium and pressure medium should be applied, and a device to be employed for this method always has a limited capacity. Further, due to the pressure prevailing in the storage vessel during use, there is a risk of explosion of the storage vessel, the more so because the blasting media to be used are highly corrosive and may hence cause damage to the storage vessel. An additional drawback of the use of a storage vessel under pressure is that after the spray nozzle has been closed, it takes a relatively long time before the pressure in the feed means to the spray nozzle has been reduced to atmospheric, entailing a great chance of after-spraying or after-dripping. Hence, the object of the invention is to provide a method for blasting by means of sand or a like blasting medium permitting hard, less hard and soft blasting, without the drawbacks of the known methods while maintaining the advantages thereof. To that end, the method according to the invention is characterized in that the blasting medium is conducted from the storage vessel by means of pump means. Because the blasting medium is conducted from the storage vessel by means of pump means, it can be dosed exactly how much blasting medium, optionally together with for instance air and/or water or a like fluid, is displaced in the direction of the spray nozzle, so that in a very simple and accurate manner the proportion between the amount of blasting medium to be used and other components can be selected and the blasting pressure can be set, while the supply of blasting medium need not be pressurized. Moreover, the advantage is achieved that when the spray nozzle is closed, the pressure in the feed means can be removed almost directly, as a consequence of which no contamination of the surroundings takes place due to after-spraying or after-dripping. As pump means, different means can be applied, such as for instance a screw conveyor or a like impeller, but it is preferred that in the method according to the invention the pump means comprises a pump with which the blasting medium is drawn from the storage vessel. A drawing pump has the advantage that it enables dosing in a simple and accurate manner. Blasting may take place in a "wet" and a "dry" manner. In the case of "wet" blasting, a blasting medium is at least substantially saturated or even supersaturated with water and this mixture is sprayed under pressure. In the case of "dry" blasting, the blasting medium is conducted to the spray nozzle in dry condition and sprayed there under pressure, the pressure being obtained through the feed of compressed air or for instance water under pressure. For environmental and health reasons, "wet" blasting has significant advantages, because the corrosive action thereof can be controlled more properly and little to no dust nuisance is caused thereby. Therefore, in further elaboration of the method according to the invention, the blasting medium is mixed in the vessel with water, and the blasting medium is preferably brought into and kept in saturated solution in the storage vessel by means of agitating or mixing means. Because the blasting medium is already mixed with water in the storage vessel, while moreover air and, if necessary, chemicals can already be admixed, a proper saturation of the blasting medium is obtained before it is pumped. If the blasting medium is lighter or heavier than water, the chances are that a separation between the blasting medium and the water occurs in the storage vessel. By utilizing mixing or agitating means in the storage vessel, this is prevented. Hence, with the method according to the invention, both blasting medium having a specific weight corresponding to that of the pressure medium, and blasting medium having a higher or lower specific weight can be used. Because the blasting medium in the storage vessel need not be pressurized, in a preferred embodiment of the method according to the invention it is possible during blasting to blast and feed blasting medium to the storage vessel at the same time. This permits the supply of blasting medium to be adjusted at will, as a consequence of which the duration of an uninterrupted blasting pass is independent of the maximum capacity of the storage vessel. In a further preferred embodiment of the method according to the invention, the optimum conditions for the surface to be blasted are selected through at least a suitable selection of the mixture of blasting medium, air and water and setting of a suitable speed of the pump. In this manner, it is possible to operate particularly accurately under optimum, always controllable conditions, allowing for instance different types of surfaces to be cleaned successively without damage. The invention further relates to a device for using the method according to the invention. The invention comprises a storage vessel, means for feeding compressed air and water, a spray nozzle and feed-through means between the storage vessel and the spray nozzle, and is according to the invention characterized in that the feed-through means comprise pump means. Because the feed-through means comprise pump means capable of conducting the blasting medium from the storage vessel and to the spray nozzle, the amount of blasting medium and the blasting pressure can be accurately controlled during blasting, enabling exact setting of the blasting conditions. In the device according to the invention, the pump means preferably comprise a pump, and in particular a peristaltic pump. A peristaltic pump has the advantage that both dry and wet substances can be pumped therewith without the pump being damaged thereby. As a result, with the device according to the invention, both dry blasting medium and wet blasting medium can be fed to the spray nozzle, optionally mixed with for instance extra air and chemicals. Hence, the device according to the invention enables both wet and dry and both hard, less hard and soft blasting. In a preferred embodiment of the device according to the invention, the device comprises a number of spray nozzles, the arrangement being such that the connected spray nozzles can be used simultaneously as well as separately. This allows different users to utilize the device simultaneously while the optimum blasting conditions set can be maintained and without thereby limiting the time wherein blasting can take place uninterruptedly. The device according to the invention is of a simple construction, requires little maintenance and can be of a relatively light design, for instance because the storage vessel can be of a significantly smaller and lighter construction than in the case of devices having a pressure vessel. The device is environmentally friendly, readily controllable and user-friendly. To explain the invention, a number of exemplary embodiments of the methods and devices will hereinafter be described with reference to the accompanying drawings. Fig. 1 schematically shows an embodiment of a simple design of a device according to the invention; Fig. 2 schematically shows an alternative embodiment of a device according to the invention, provided with different feed and control means. The device according to Figs 1 and 2 comprises a storage vessel 1, a pump 2, a distribution block 3, a compressor 4, an air control valve 5 and a spray nozzle 6. The storage vessel 1 is funnel-shaped and comprises, at its lower side 7, a suction line 8 whose other side is connected to the suction side of the pump 2. Connected at the outlet side of the pump 2 is a feed-through line 9 which connects the pump 2 with the distribution block 3. At its pressure side, the compressor 4 comprises a pressure line 10 which connects the compressor 4 with the distribution block 3. In the pressure line 10 the air control valve 5 is accommodated. In the distribution block 3, the feed-through line 9 and the pressure line 10 jointly connect to the blast hose 11 terminating in the spray nozzle 6. The device according to Fig. 1 can be used as follows. From the open upper side 12 of the storage vessel 1, a blasting medium is thrown into it. This may take place prior to as well as during the use of the device, because the storage vessel 1 is always in or can always be brought into open communication with the surroundings. After all, no pressure is built up in the storage vessel 1. As blasting medium, preferably silicon-free or silicon-poor sand is used, but other blasting media such as glass beads can be used as well. The blasting medium can be inserted dry as well as wet, and chemicals, for instance, can also be fed together with the blasting medium. By switching on the pump 2, blasting medium is sucked from the storage vessel 1 and passed in the direction of the distribution block 3. At the same time, compressed air is fed to the distribution block 3 by means of the compressor 4. In the distribution block 3, the flow of blasting medium and the flow of compressed air are mixed and conducted through the blast hose 11 to the spray nozzle 6, where the blasting medium is sprayed under high pressure. By controlling the speed of the pump 2 the magnitude of the flow of blasting medium is set, and by controlling the air control valve 5 the magnitude of the flow of compressed air is set. This enables the composition of the blast sprayed to be set in a particularly simple and accurate manner, while it moreover enables both wet and dry blasting, and both hard, less hard and soft blasting. By changing the speed of the pump 2 and the position of the air control valve 5, it is even possible to adjust the abrasive action of the blasting device during blasting. Fig. 2 shows an alternative embodiment of a device according to the invention, including water and air feed means and control means. This device is suitable in particular for wet blasting. The water circuit W of the device is built up as follows. Via a water supply line 14, a supply of water is created and, if required, maintained in a water tank 13. The water supply line can be connected to a water line system permanently or can be coupled thereto according to the need. Water can also be supplied in various other manners. Connected to the water tank 13 is a water discharge line 15, connected, via a filter 16 and a water pump 17, with a pressure regulating valve 18. From the pressure regulating valve 18, a water return line 19 leads back to the water tank 13, a first water pressure line 20 leads to the storage vessel 1 and a second water pressure line 21 leads to the blast hose 11. Both in the first water pressure line 20 and the second water pressure line 21, a stop valve 22' and 21' ' respectively, and a water control valve 23' and 23' ' respectively are accommodated. Moreover, accommodated in the second water pressure line 21 is a non-return valve 24 so that water can flow only from the second water pressure line 21 to the blast hose 11 and not the other way round. The first water pressure line 20 opens into the storage vessel near the lower side 7 thereof. The air circuit L of the device is built up as follows. Accommodated in the pressure line 10 between the compressor 4 and the air control valve 5 is an air stop valve 25 with which the air supply to the distribution block 3 can be shut off. Between the compressor 4 and the air stop valve 25, a distribution line is connected to the pressure line. Via a distribution piece 27, the distribution line 26 blends with a storage vessel air line 28 and a pump air line 29. Via a second air control valve 30 and a second air stop valve 31, the storage vessel air line 28 terminates in an air spray nozzle 32 provided at the bottom of the storage vessel 1, which air spray nozzle 32 is preferably slightly inclined relative to the centre longitudinal axis of the storage vessel 1. Via an air pressure reducing valve 33 and a third air control valve 34, the pump air line 29 opens into the suction line 8 near the suction side of the pump 2. The device according to Fig. 2 can be used in a manner corresponding to the manner as described in respect of the device according to Fig. 1, with the following additions. In the device according to Fig. 2, water is added to the blasting medium at the bottom of the storage vessel via the first water pressure line 20, in such a manner that the blasting medium is completely saturated or supersaturated. By means of the storage vessel air line 28, air is simultaneously blown into the mixture of blasting medium and water, which keeps the mixture in motion and prevents a separation between the water and the blasting medium. As a matter of fact, this can also be effected through different means, such as mixing or agitating means at the bottom of the storage vessel or recirculation of the mixture through a circulating line. By means of the pump 2, the mixture of water and blasting medium and, optionally, air, is drawn from the storage vessel 1 at its lower side, while at the same time air can be admixed at will via the pump air line 29. Subsequently, the thus obtained mixture of water, air and blasting medium is mixed in the distribution block 3 and put under high pressure by means of the flow of compressed air that is fed via the pressure line 10, and subsequently forced through the blast hose 11. Via the second water pressure line 21, extra water can further be admixed in the blast hose, so that the proportion of water. air and blasting medium in the flow to be sprayed can be influenced. Subsequently, after the spray nozzle has been opened and aimed, the intended blasting effect can be produced. To obtain an optimum result, the device according to Fig. 2 can be set as follows. After the dry blasting medium has been introduced into the storage vessel 1, the water stop valve 22' is opened and the control valve 23' is set so that the desired amount of water is added to the blasting medium. This may take place discretely or continuously with a fixed or controllable flow rate. By opening the second air stop valve 31 and setting the second air control valve 30, a flow of air is blown through the mixture of water and blasting medium via the air spray nozzle 32 at the bottom of the storage vessel 1, which keeps the mixture in motion and homogenous. The pump 2 is switched on and its speed is set, as a result of which the desired amount of mixture per unit of time is drawn from the storage vessel 1. By changing the speed, this flow rate can be adjusted, and moreover, by means of the air pressure reducing valve 33 and the third air control valve 34, a dosed amount of air can be fed to the mixture flow, as a result of which less mixture will be drawn from the storage vessel 1 per unit of time and, simultaneously, the composition of the relevant mixture of water, air and blasting medium will be changed; more air. In the distribution block 3, the flow of compressed air is added to the mixture flow, and the flow rate of the compressed air can be controlled by opening the first air stop valve 25 and setting the first air control valve 5. Subsequently, in the blast hose 11, secondary water can further be fed via the second water pressure line 21 by opening the second water stop valve 22' ', while the secondary water flow can be controlled by means of the second water control valve 23''. Due to the feed of the secondary water flow, the pressure in the blast hose 11 is further increased and at the same time the composition of the flow of water, air and blasting medium is changed; more water. With the device according to Fig. 2, almost any composition of the flow of mixture to be sprayed can be obtained; from completely or almost completely dry to very much water with no or only very little blasting medium, constantly permitting creation of various blasting conditions, while the blasting pressure can moreover be controlled continuously. The device may comprise an electronic control system by means of which for instance the setting of the water and air stop valves, the water and air control valves, air and water pressure reducing valve and the speed of the pump can be controlled preferably from the nozzle, so that during operation the optimum setting can always be selected without the work having to be interrupted therefor. For checking purposes, manometers are provided at various locations in the water circuit W and the air circuit L. The pump 2 is preferably a peristaltic pump. Such a pump has the advantage that it enables air, dry blasting medium or water, as well as a mixture of two or three of these components, to be pumped, with or without the addition of different chemicals, without the pump being damaged thereby. The pump is sturdy, has sufficient capacity and is insusceptible to trouble. Moreover, the speed and, accordingly, the pump volume per unit of time can readily be controlled. In the device according to the invention, different blast hoses 11 and associated spray nozzles 6 can be connected to the distribution block 3 and used, without the blasting qualities of the device being adversely affected thereby. Hence, with this device it is possible to carry out blasting activities on mutually different surfaces without damaging these surfaces and regardless of the nature of the surface, in principle for an unlimited time and with different people simultaneously. Because the storage vessel 1 need not be pressurized and, if so desired, can be replenished continuously, it may be built up of all sorts of material, such as metal or plastic, and the storage vessel need not be large, permitting a compact and light construction of the device. The drive of the device can be realized in various manners, such as for instance by hydraulic means, an electomotor or a combustion motor. The invention is by no means limited to the exemplary embodiments given in the drawing and the specification. Many adaptations are possible within the purview of the invention. For instance, other agitating and mixing means can be applied in the storage vessel, as a consequence of which the storage vessel air line can possibly be omitted, and the storage vessel can of course have various other forms. As pump means, a different pump can be applied having for instance a controllable passage instead of or together with a controllable speed, or a different positively acting transporting device can be applied. Further, pressure in the different lines can also be generated by means of water pressure instead of air pressure, for instance through the interposition of a water pressure pump driven by air or otherwise. The different air and water lines can also be connected at other locations.

Claims: CLAIMS 1. A method for blasting with sand or a like blasting medium, wherein the blasting medium is conducted from a storage vessel to a spray nozzle and distributed by means of a pressure medium such as compressed air or water, characterized in that the blasting medium is conducted from the storage vessel by means of pump means. 2. A method according to claim 1, characterized in that the blasting medium is drawn from the storage vessel by means of the pump means. 3. A method according to claim 1 or 2, characterized in that the blasting medium in the vessel is mixed with water. 4. A method according to claim 3, characterized in that the blasting medium is kept in saturated solution in the storage vessel by means of agitating or mixing means. 5. A method according to any one of the preceding claims, characterized in that during blasting, blasting and feeding blasting medium into the storage vessel take place simultaneously. 6. A method for blasting surfaces of for instance stone or steel, characterized in that the optimum conditions for the surface to be blasted are selected through at least a suitable selection of the mixture of blasting medium, air and water and setting of a suitable pump discharge of the pump means. 7. A'device for use in a method according to any one of the preceding claims, comprising a storage vessel, means for feeding compressed air and water, a spray nozzle and feed- through means between the storage vessel and the spray nozzle, characterized in that the feed-through means comprise at least pump means. 8. A device according to claim 7, characterized in that the pump means comprise a pump. 9. A device according to claim 8, characterized in that the pump is a peristaltic pump. 10. A device according to claim 7, 8 or 9, characterized in that during use, the storage vessel is in or can be brought into open communication with the surroundings. 11. A device according to any one of claims 7-10, characterized in that the storage vessel comprises agitating and mixing means. 12. A device according to any one of claims 7-11, characterized in that the device comprises control means for the dosed feed of compressed air and/or water to both sides of the pump. 13. A device according to any one of claims 7-12, characterized in that the device comprises a number of spray nozzles, the arrangement being such that the connected spray nozzles can be used simultaneously as well as separately.

Inventors: DEMKES JOHAN WILLEM, MELLENDIJK DICK WILLEM, DEMKES, JOHAN, WILLEM, MELLENDIJK, DICK, WILLEM
Applicants: WATERKRACHT BV, WATERKRACHT B.V.
Application year: 1994
Main classification: B24C7
IPC codes: B24C7